The present invention relates in general to devices which provide for the selective adjustment and positioning of components relative to one another.
In particular, it relates to the vertical adjustment of a chair backrest relative to the chair seat such that the backrest can be manually raised or lowered to any of a plurality of selectable positions and releasably locked therein.
As will be seen, the device is also ideally suited for other purposes, such as shelves and windows due to its simplicity and economy in manufacture.
In the prior art, chair backrest height adjustment has been accomplished in some chairs by the use of operabale screws that secure a slidably adjustable backrest on an upwardly extending J-bar which is part of the chair frame. In other chairs, manually operable rack and pinion types or linear ratchets with spring biased locking arms and pins provide for backrest adjustment. Such prior devices are complex in contruction, requiring precise construction, injection molded parts and springs, and are therefore costly to manufacture, trouble prone, unreliable and visually unattractive.
The device and object of the present invention provides for the manual vertical adjustment of a chair backrest relative to the chair seat at any of a plurality of releasably lockable positions within a predetermined range. As will appear clear in the subsequent specification, the device is, due to its inherent simplicity, highly suitable for adaptation to other height adjusting purposes, such as in shelves, windows and other items requiring reliable and economical means. In a chair, the device comprises a slide plate which is rigidly secured to the chair frame or J-bar and a track plate which is rigidly secured to the backrest and slidably mounted for vertical movement on the slide plate. The slide plate and track plate are slidably coupled to each other by tongue and groove connection means along their vertical edges. Both the slide plate and the track plate are provided with slots exhibiting cam surfaces. The slide plate slot exhibits a cam surface so designed as to provide at least three distinct positions for the lock pin, these being: a first unlocked position, a second standby position, a third locked position; the lock pin being free to slide and roll along the slot cam surface of the slide plate in response to the action of the cam surfaces of the track plate slot. The track plate slot exhibits cam surfaces such that on one side the cam surface comprises a series of notches made to include a corresponding series of incline plane cam surfaces so that upward vertical displacement of the slide plate relative to the track plate causes the lock pin to roll along the incline plane surface of a notch with a resultant lateral displacement onto the standby position on the cam surface of the slide plate slot. As the notch passes over center of the lock pin, the next notch is aligned with a portion of the slide plate slot so that the lock pin is free to occupy the notch. At this point, downward movement of the track plate relative to the slide plate is not possible and the device is in the locked position. Continuous vertical adjustment in the upward direction is possible for as many positions as notches are provided on the track plate slot. The last notch is provided with an extended incline plane cam surface so as to guide the lock pin and cause it to roll onto the unlocked position on the cam surface of the slide plate slot, whereupon the track plate is free to vertically slide in the downward direction. As the track plate reaches its lowermost vertical position, a cam surface on the track plate slot, at the upper end of the slot, causes the lock pin to freely roll from the unlocked position to the locked position corresponding to the first notch on the track plate slot and the cycle may be repeated at will.
The advantages of the device are numerous. The device is extremely easy to operate as all that is required is to lift the backrest of the chair only slightly to the next locked position and locking takes place automatically upon release of the backrest. Intrinsic to the design of the device is a high degree of reliability as it does not make use of springs or other biasing means prone to failure and relies only on cam action and gravity for positioning of the lock pin. Therefore the device is extremely economical to manufacture as the number of parts is only a maximum of three and the need for complex injection molded parts is eliminated. Furthermore, the device is highly suitable for manufacture by metal stamping and forming techniques. Because of the simplicity of the device it is also possible and highly desirable to make the slide plate, which contains only a short cam slot, be the J-bar itself, thus eliminating yet another part and providing the entire assembly with a very low profile; a highly desirable feature for chair manufacturers and designers. Further yet the device may be provided with any plurality of locking pins and the slide plate with any plurality of cam slots so as to obtain different positional strokes of one plate relative to the other, or to provide for added locking elements. The economical means of manufacture provided by the device, object of the present invention, make it ideally suited for providing reliable means of vertical adjustment to items where cost has thus far prevented their use or where an easily operable device is imperative. One such item may be all type of shelving, where it is often desirable to adjust the shelf height with facility and ease. Such shelving may be of the type required in household ovens, refrigerators, and casegoods. In addition the device is ideally suited for the reliable, safe and economical adjustment of windows, as opposed to the present art use of troublesome and unpredictable friction devices.